A large number of liquid crystal displays (LCDs) utilizing optical (refractive index) anisotropy (Δn) (hereinafter sometimes simply referred to as Δn) and dielectric anisotropy (Δ∈) (hereinafter sometimes simply referred to as Δ∈) characteristic of liquid crystal compounds have been produced. LCDs are widely applied to watches, calculators, various measuring instruments, automotive panels, word processors, electronic notebooks, cell phones, printers, computers, TV sets, etc. and in ever increasing demand A liquid crystal compound exhibits an inherent liquid crystal phase between a solid phase and a liquid phase. Liquid crystal phases are roughly classified into a nematic phase, a smectic phase, and a cholesteric phase. For display applications, a nematic phase is most widely used. Display modes applied to LCDs typically include twist nematic (TN), super twist nematic (STN), dynamic scatter (DS), guest host (GH), in-plane switching (IPS), optically compensated birefringence (OCB), electrically controlled birefringence (ECB), vertical alignment (VA), color super homeotropic (CSH), and ferroelectric liquid crystal (FLC). As drive systems, a multiplex drive system has now become common, replacing a traditional static drive system. Passive matrix LCDs and, more lately, active matrix (AM) LCDs driven by thin film transistors (TFTs) or MIMs are prevailing.
Conventional AM-LCDs mostly use a TN mode liquid crystal cell in which molecules of a liquid crystal material having a positive dielectric anisotropy (Δ∈) are aligned to be in parallel to the substrates and twisted by 90 degrees between the opposing substrates. However, the TN mode LCDs have a disadvantage of a narrow viewing angle, and various studies have been made to increase the viewing angle.
VA mode LCDs, particularly MVA and EVA mode LCDs described in non-patent documents 1 and 2 (see below) have been developed as an alternative to TN mode LCDs and succeeded in greatly improving viewing angle characteristics. In these VA mode LCDs, molecules of a liquid crystal material having negative dielectric anisotropy between two substrate are aligned perpendicular to the substrates and, with a voltage applied, the tilt direction of the liquid crystal directors are controlled by ribs or slits made on the surface of the substrates. Recently, an LCD made by using a liquid crystal material containing a monomer or an oligomer polymerizable on light or heat application has been proposed as in patent document 1 (see below). An LCD of this type is produced by sealing the liquid crystal material in between two substrates and polymerizing the polymerizable component while adjusting the voltage applied to the liquid crystal layer thereby to decide the alignment direction of the liquid crystal molecules.
Thus studies to improve the viewing angle characteristics are well underway, providing practical big LCD panels for notebook or desktop computers and even bigger display media represented by LCD-TV monitors. However, there is a problem with these LCDs that they are slow in response to an electric field, and demands for rapid response are still high. LCDs used to display moving images, such as LCD-TVs, are particularly required to exhibit a rapid response. In order to achieve high definition and high display qualities with an LCD, it is necessary to develop and use a liquid crystal material having rapid response characteristics.
In order to obtain a good contrast ratio with an LCD driven at a constant frame rate, it is desirable for the LCD to have a high voltage holding ratio (voltage holding ratio during a frame period, hereinafter abbreviated as VHR). In the case where a liquid crystal material is given energy, such as light or heat, as in patent document 1, the compound can deteriorate to cause reduction in VHR.
Patent document 1 discloses a VA mode LCD with reduced burn-in and a composition used therefor. Patent document 2 below discloses an alignment film providing a VA mode LCD having a high VHR. With these techniques, nevertheless, a satisfactory response speed is not obtained. Patent documents 3 and 4 below disclose a VA mode liquid crystal composition but have no mention of the use of a polymerizable liquid crystal compound having a (meth)acryloyl group as a polymerizable group. Patent document 5 below proposes a polymerizable liquid crystal compound but neither describes nor suggests the use of the compound in a liquid crystal composition having negative dielectric anisotropy (Δ∈).
Patent document 1: JP 2003-307720A
Patent document 2: JP 2006-215184A
Patent document 3: JP 2005-48007A
Patent document 4: JP 2007-23071A
Patent document 5: JP 2007-119415A
Non-patent document 1: EKISHO, vol. 3, No. 2, p. 117 (1999)
Non-patent document 2: EKISHO, vol. 3, No. 4, p. 272 (1999)